High early strength cementitious binders have been used in the past to repair cementitious structures, or as components of cementitious compositions to form structures. In one class of these materials, ammonium phosphates are used to prepare binder materials in reaction with magnesium ion-providing materials, such as MgO. International Patent Publication WO 96/35647 discloses a mechanism by which potassium struvite was prepared from an ammonium phosphate reactant. Some have proposed the use of other metal phosphates in conjunction with or as a replacement of ammonium phosphate, such as phosphate acid salts of Al, Ca, Mg or Na.
U.S. Pat. No. 2,522,548 discloses the production of refractory molds for metal casting made with phosphate binders produced from a metal oxide or hydroxide (Ca, Mg or Zn), a primary metal phosphate (Mg, Ca, Zn, Mn, Al or Fe), and a primary alkali metal phosphate (Na or K). The binder may be combined with fillers and retarders.
U.S. Pat. No. 4,444,594 discloses acid cured inorganic compositions suitable for a binder material compatible with mineral wool, for application in ceiling tiles. The binder is produced by reacting MgO, an acid phosphate, chloride or sulfate salt, an amino alcohol and water. Fillers can be added to the binder. The acid phosphate can be ammonium phosphate (preferred), sodium phosphate and potassium phosphate.
One problem encountered with the use of conventional repair binders or mortars, is that they usually contain ammonium phosphate hydrate as a component, for reaction with an alkaline earth oxide or hydroxide such as MgO or MgOH in water to form struvite. The reaction of the ammonium phosphate salt with the alkaline earth metal drives off ammonia as a gas, causing foaming and creating an unpleasant environmental odor. The use of such binders or cements indoors is severely limited.
A further problem with conventional materials is that the reaction between the alkaline earth metal ion and the ammonium phosphate salt is so fast, that the binder sets almost immediately, and limits the ability of the workman to "finish" the product in place. Setting retarders are therefore needed to permit working of the mixture to effectively treat the structure in need of repair.